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| author | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
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| committer | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-07-20 20:00:05 +0100 |
| commit | 3ef782d3745ea8f25a3151561a3cfb882190210e (patch) | |
| tree | 86b9c2f5fde051dd0bced99b3fc9f5a3ba08db69 /docs/programmer_reference/stl_primitive_rw.html | |
| download | berkeleydb-3ef782d3745ea8f25a3151561a3cfb882190210e.tar.gz | |
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diff --git a/docs/programmer_reference/stl_primitive_rw.html b/docs/programmer_reference/stl_primitive_rw.html new file mode 100644 index 00000000..a17d1d3f --- /dev/null +++ b/docs/programmer_reference/stl_primitive_rw.html @@ -0,0 +1,185 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <title>Working with primitive types</title> + <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> + <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> + <link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> + <link rel="up" href="stl.html" title="Chapter 7. Standard Template Library API" /> + <link rel="prev" href="stl_mt_usage.html" title="Using dbstl in multithreaded applications" /> + <link rel="next" href="stl_complex_rw.html" title="Store and Retrieve data or objects of complex types" /> + </head> + <body> + <div xmlns="" class="navheader"> + <div class="libver"> + <p>Library Version 11.2.5.3</p> + </div> + <table width="100%" summary="Navigation header"> + <tr> + <th colspan="3" align="center">Working with primitive types </th> + </tr> + <tr> + <td width="20%" align="left"><a accesskey="p" href="stl_mt_usage.html">Prev</a> </td> + <th width="60%" align="center">Chapter 7. Standard Template Library API</th> + <td width="20%" align="right"> <a accesskey="n" href="stl_complex_rw.html">Next</a></td> + </tr> + </table> + <hr /> + </div> + <div class="sect1" lang="en" xml:lang="en"> + <div class="titlepage"> + <div> + <div> + <h2 class="title" style="clear: both"><a id="stl_primitive_rw"></a>Working with primitive types </h2> + </div> + </div> + </div> + <div class="toc"> + <dl> + <dt> + <span class="sect2"> + <a href="stl_primitive_rw.html#idp1288424">Storing strings</a> + </span> + </dt> + </dl> + </div> + <p> + To store simple primitive types such as <code class="literal">int</code>, + <code class="literal">long</code>, <code class="literal">double</code>, and so forth, an + additional type parameter for the container class + templates is needed. For example, to store an <code class="literal">int</code> + in a <code class="classname">db_vector</code>, use this container class: +</p> + <pre class="programlisting">db_vector<int, ElementHolder<int> >;</pre> + <p> + To map integers to doubles, use this: +</p> + <pre class="programlisting">db_map<int, double, ElementHolder<double> >;</pre> + <p> + To store a <code class="literal">char*</code> string with <code class="literal">long</code> keys, + use this: +</p> + <pre class="programlisting">db_map<long, char*, ElementHolder<char*> >;</pre> + <p> + Use this for <code class="literal">const char*</code> strings: +</p> + <pre class="programlisting">db_map<long, const char*, ElementHolder<const char*> >;</pre> + <p> + To map one const string to another, use this type: +</p> + <pre class="programlisting">db_map<const char*, const char*, ElementHolder<const char*> >;</pre> + <p> + The <code class="methodname">StlAdvancedFeaturesExample::primitive()</code> method demonstrates more of these examples. +</p> + <div class="sect2" lang="en" xml:lang="en"> + <div class="titlepage"> + <div> + <div> + <h3 class="title"><a id="idp1288424"></a>Storing strings</h3> + </div> + </div> + </div> + <p> + For <code class="literal">char*</code> and <code class="literal">wchar_t*</code> strings, + <code class="methodname">_DB_STL_StoreElement()</code> must be called + following partial or total modifications before iterator movement, + <code class="literal">container::operator[]</code> or + <code class="literal">iterator::operator*/-></code> calls. Without the + <code class="methodname">_DB_STL_StoreElement()</code> call, the modified + change will be lost. If storing an new value like this: +</p> + <pre class="programlisting">*iterator = new_char_star_string;</pre> + <p> + the call to <code class="methodname">_DB_STL_StoreElement()</code> is not needed. +</p> + <p> + Note that passing a NULL pointer to a container of + <code class="literal">char*</code> type or passing a + <code class="classname">std::string</code> with no contents at all will insert + an empty string of zero length into the database. +</p> + <p> + The string returned from a container will not live beyond the next + iterator movement call, <code class="literal">container::operator[]</code> or + <code class="literal">iterator::operator*/-></code> call. +</p> + <p> + + A <span class="bold"><strong>db_map::value_type::second_type</strong></span> or + <span class="bold"><strong>db_map::datatype_wrap</strong></span> should be used + to hold a reference to a <code class="literal">container::operator[]</code> + return value. Then the reference should be used for repeated + references to that value. The *iterator is of type + <code class="literal">ElementHolder<char *></code>, which can be automatically converted to a + <code class="literal">char *</code> pointer using its type conversion operator. + Wherever an auto conversion is done by the compiler, the conversion + operator of <code class="literal">ElementHolder<T></code> is called. This + avoids almost all explicit conversions, except for two use cases: + +</p> + <div class="orderedlist"> + <ol type="1"> + <li> + <p> + The *iterator is used as a "..." parameter like this: + </p> + <pre class="programlisting">printf("this is the special case %s", *iterator);</pre> + <p> + This compiles but causes errors. Instead, an explicit cast + should be used: + </p> + <pre class="programlisting">printf("this is the special case %s", (char *)*iterator);</pre> + </li> + <li> + <p> + For some old compilers, such as gcc3.4.6, the *iterator cannot be + used with the ternary <code class="literal">?</code> operator, like + this: + </p> + <pre class="programlisting">expr ? *iterator : var</pre> + <p> + Even when <span class="bold"><strong>var</strong></span> is the same + type as the iterator's <code class="literal">value_type</code>, the + compiler fails to perform an auto conversion. + </p> + </li> + </ol> + </div> + <p> + When using <code class="classname">std::string</code> or + <code class="classname">std::wstring</code> as the data type for dbstl + containers — that is, <code class="classname">db_vector<string></code>, + and <code class="classname">db_map<string, wstring></code> — the + string's content rather than the string object itself is stored in order + to maintain persistence. +</p> + <p> + You can find example code demonstrating string storage in the + <code class="methodname">StlAdvancedFeaturesExample::char_star_string_storage()</code> and + <code class="methodname">StlAdvancedFeaturesExample::storing_std_strings()</code> methods. +</p> + </div> + </div> + <div class="navfooter"> + <hr /> + <table width="100%" summary="Navigation footer"> + <tr> + <td width="40%" align="left"><a accesskey="p" href="stl_mt_usage.html">Prev</a> </td> + <td width="20%" align="center"> + <a accesskey="u" href="stl.html">Up</a> + </td> + <td width="40%" align="right"> <a accesskey="n" href="stl_complex_rw.html">Next</a></td> + </tr> + <tr> + <td width="40%" align="left" valign="top">Using dbstl in multithreaded applications </td> + <td width="20%" align="center"> + <a accesskey="h" href="index.html">Home</a> + </td> + <td width="40%" align="right" valign="top"> Store and Retrieve data or objects of complex types </td> + </tr> + </table> + </div> + </body> +</html> |